A pouch (bag) that is formed of a film produced using a flexible material such as polyvinyl chloride, polyethylene, or polypropylene has been known as an injection container. A pouch allows easy drainage of a fluid contained therein at atmospheric pressure, and is highly safe due to flexibility. Therefore, a pouch has been generally used as an infusion container. A multilayer film that forms a pouch is required to exhibits excellent flexibility, transparency, heat resistance, hygienic properties, mechanical strength, gas barrier capability, workability, and the like from the viewpoint of a material.
In recent years, a reduction in the amount of waste has been desired to deal with environmental issues and hospital issues, and a reduction in volume has been required for medical containers. Therefore, an injection bag that meets the above quality requirements, and can be disposed of in a non-bulky manner has been desired.
Soft polyvinyl chloride to which a plasticizer is added has been used as a material for forming a pouch. Soft polyvinyl chloride exhibits excellent flexibility, heat resistance, transparency, workability, gas barrier capability, and the like. However, a plasticizer, a stabilizer, a residual monomer, and the like included in polyvinyl chloride may be eluted into a fluid contained in a pouch, and it has been pointed out that dioxine may be produced during incineration after disposal. In order to deal with the above problems, a pouch formed of a polyolefin-based resin instead of polyvinyl chloride has been proposed from the viewpoint of hygienic properties and safety.
However, since a polyolefin-based resin exhibits a poor gas barrier capability, oxygen in air may pass through the pouch, and the drug solution may change in quality. The water vapor pressure that has been saturated inside the pouch normally causes a difference in partial pressure of nitrogen and partial pressure of oxygen between the inside and the outside of the pouch. When using a pouch formed of a polyolefin-based resin that exhibits a poor gas barrier capability, the volume inside the pouch may increase due to the differential pressure (osmotic pressure), and the drainage capability and the like may deteriorate due to expansion of the pouch. It is known that the burden imposed on the body can be reduced by adjusting the pH of an injection or a peritoneal dialysis fluid using bicarbonate ions that are normally present in the body. However, since a polyolefin-based resin exhibits a poor gas barrier capability, carbonic acid is removed during heat sterilization at a temperature of more than 100° C.
As a pouch-forming material that may solve the above problems, an infusion bag formed of a four-layer multilayer film consisting of polyolefin-based resin layer/adhesive resin layer/polyamide layer/low-water-permeable resin layer (where “/” indicates the boundary between two layers (hereinafter the same)) has been proposed (see JP-A-60-55958, for example). An injection bag formed of a multilayer film in which a polyamide resin is used for an intermediate layer has also been proposed (see JP-A-2002-35084, for example).
However, an injection bag has not been known that exhibits a practical gas barrier capability, and meets the maximum UV absorbance standard of the Test Methods for Plastic Containers (elution test) specified in the Japanese Pharmacopoeia. This is because a water-soluble monomer such as epsilon-caprolactam and a water-soluble low-molecular-weight polymer are eluted from the polyamide resin used for the intermediate layer or the like of the multilayer film. When the thickness of the polyamide resin layer is increased to achieve a practical barrier capability, a large amount of monomer and low-molecular-weight polymer is eluted into the fluid contained in the injection bag, and the maximum UV absorbance measured by the Test Methods for Plastic Containers specified in the Japanese Pharmacopoeia exceeds 0.08.